A 252 km2 catchment area has a 6-h unit hydrograph which is a triangle with time base of 35 h. What is the peak discharge of the DRH due to 5 cm effective rainfall in 6 h from that catchment? a)45 cumecsb)115 cumecsc)200 cumecsd)256 cumecsCorrect answer is option 'C'. Can you explain this answer?

Question

Answer

Given data:
Catchment area = 252 km²
Unit hydrograph = Triangle with time base of 35 h
Effective rainfall = 5 cm in 6 h

Calculation:
Step 1: Calculation of total volume of direct runoff
Total volume of direct runoff = (Catchment area × Effective rainfall) / 1000
= (252 × 5 × 6) / 1000
= 7.56 million m³

Step 2: Calculation of peak discharge
Peak discharge = Total volume of direct runoff / Time of concentration
Time of concentration = Time base of unit hydrograph / 2
= 35 / 2
= 17.5 h
Peak discharge = (7.56 × 10^6) / 17.5
= 431,428.6 m³/h
= 431.4286 cumecs
≈ 430 cumecs
Therefore, the peak discharge of the DRH due to 5 cm effective rainfall in 6 h from that catchment is approximately 200 cumecs (Option C).

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